A preliminary study on the Gorgan-Rud (River) aquatic life: A limnological approach (from Gonbad to Gorgan-Dam). (In Farsi, with English Summary).

Although Gorgan-Rud is one of the most important rivers of the region from agriculture, aquaculture, and fish migration standpoint, a thorough limnological study has not yet been conducted on the river and that is more true with the biological aspects of a limnological work. Therefore, a one-year study was proposed to cover four different seasons. The main aims were to gather information on physical, chemical, and biological aspects of the river. The ecological relationships and possible proposal to improve the situation were also our interest. Seven stations were selected: 1. the dam outlet, 2. the reservoir, 3. Bibi-Shirvan, 4. Yasi-Tapeh, 5. Ghazaghli, 6. Gedam-Abad, and 6. Hajilar-Ghallah. Sampling was carried out at four stations (i.e., 1, 3, 4, and 5) regularly, but occasionally at the other three stations. Physico-chemical analysis showed that Gorgan-Rud water, except for a short time in spring was not suitable for human consumption, but it seems to be suitable for livestock, except occasional cases. For agriculture purposes, Water in stations 1 and 2 was considered good in spring and rated medium in other seasons. In general water quality from station 1 to 6, where Gonbad outlet exists, declines continuously. Changes in the water pH were quite irregular and varied from 6.3 to 7.9, with an average of 7.1. Electric conductivity (EC), varied greatly from 667-10000 µm/cm with an average of 875 µm/cm. Chlorides, especially NaCl were the most abundant of soluble salts. There was an inverse relationship between TDS and the water volume. At station 5, TDS showed a high figure of 4300 mg/l in the summer, when water was the lowest, and a low figure of 500 mg/l in the spring, when the water was the highest. The comparative figure for station 1 was 21 mg/l. Water volume at station 5 which is the dam inlet, varied from 2 to 75 m3/s. Almost 52% of the sediments enter dam reservoir during a high flood. TSS also changes with the river conditions. Its lowest figure was recorded in the first station and its value increased in all other stations. Except for the second station, water temperature varied greatly and on the average was 8-33 oC, during the study period. The most numerous phytoplanktons were Chlorophyceae, Diatoma, Euglenophyceae, and Cyanophyceae, respectively. Ankistrodesmus, Ulotrix, Clatrocystis, Eudorina, Spirogyra, Pediastrum, and Bothriococcus were the most important green algae. Diatomus, Synedra, Fragilaria, Navicula, and Gyrosigma, were the most important diatoms. Among Euglenophyceae, Euglena, and among blue-green algae, Microcystis and Spirolina were the most abundant genera. Copepoda ( Cyclops; Diaptomus; Canthocampus; Nauplius), Nematoda, and Rotifera (Asplanchna; Trichocerca; Brachionus; Filina), and Protozoa (Bursaria; Paramcium; Charchesium) comprised the most important zooplanktons. Diptera (Chironomus; Eristalis; Thurauia; Tipula), Annelidae (Tubifex; Lumbricula), Ephemeroptera, Odonata, Mollusca (Gastropoda, Bivalvia), and Coleoptera were the major benthos taxa. Cyprinus carpio, Barbus barbus, Alburnus spp., Cobitis taenia, Gambusia affinis, and Carassius carassius were the major fish species. Cobitis taenia and Carassius carassius, were relatively the most abundant species. There were other animals recorded in the region, including Astacus sp., Natrix natrix, Emys sp., and Rana sp. Water quality was tested based on two different methods. Gorgan-Rud water was rated "Polluted" based on Trent's method and in the range of "Mesosaprobic & Polysaprobic" according to the Marson's (Saprobic) system.